The use of compressible fluid jets operating across the surface of a moist paper web and discharging into a suction box to dewater and/or to transfer the web from one foraminous surface to another are well known in the art. U.S. Pat. Nos. 1,549,338 issued to Tompkins on Aug. 11, 1925, 1,843,656 issued to Tompkins et al. on Feb. 2, 1932, 3,301,746 issued to Sanford et al. on Jan. 31, 1967, and 3,879,257 issued to Gentile et al. on Apr. 22, 1975 are representative of such prior art structures. It is noteworthy, however, that in such prior art apparatus the nozzle means are in each case spaced a distance away from the web and the foraminous member on which the web is supported. There is no seal between the slotted nozzle and the foraminous web supporting member. The lack of intimate contact between the nozzle slot and the foraminous supporting member and the resultant leakage of compressible fluid prevent direct pressure application to the composite structure comprising the foraminous supporting members and the moist paper web constrained therebetween. Such prior art nozzles blowing against the web change pressure in the nozzle header to velocity through the nozzle and then back to pressure at the interface with the foraminous supporting members and the moist paper web.
Prior art devices which have the capability of applying a high pressure compressible fluid directly across the surface of the web are also known. U.S. Pat. No. 3,284,285 issued to Holden on Nov. 8, 1966 discloses a perforated roll which acts to constrain a moist paper web against a foraminous fabric while discharging high pressure air from its periphery and into a suction box located adjacent the lowermost surface of the foraminous web supporting member. U.S. Pat. No. 3,657,069 issued to Candor et al. on Apr. 19, 1972 employs a movable nozzle means in the form of a continous belt operating about a pair of rolls. The belt is internally pressurized and has a plurality of openings along its periphery which serve to discharge high pressure air across the moving, moist paper web and into a suction box located beneath the surface of a foraminous web supporting member. U.S. Pat. No. 2,753,766 issued to Simpson on July 10, 1956 discloses another prior art perforate belt apparatus for web dewatering.
U.S. Pat. No. 3,447,247 issued to Daane on June 3, 1969 discloses a low-pressure apparatus for removing moisture from a lightweight paper web by impinging drying air on the web at high velocity, whereby the momentum of the high velocity air causes it to penetrate the web. According to the teachings of Daane, penetration of the web by the high velocity air increases the exposure of internal web fibers to the evaporative effect of the air, which is preferably heated, and also physically blows or pushes moisture particles through and out of the web. The apparatus of Daane preferably employs a plurality of slotted nozzles in spaced, generally parallel adjacency to the surface of an unconstrained web opposite the foraminous support member, said nozzles preferably operating at pressures on the order of about 30 inches of water. U.S. Pat. No. 3,810,818 issued to Arledter on May 14, 1974 discloses a twin wire papermaking machine having suction boxes within the loop of one wire and hot air blast boxes within the other arranged in serpentine fashion. The boxes employ a perforated convex domed wire supporting wall and are preferably utilized in combination with one or more elements selected from the group comprising foils, suction cylinders, press cylinders, grooved cylinders, and the like.
The prior art completely fails, however, to teach or disclose a fixed, slotted nozzle which discharges a high pressure jet of compressible fluid and which forms a seal against the innermost surface of a traveling formainous support member to dewater a moist paper web secured between said first traveling foraminous support member and a second traveling foraminous support member, said support members and said fibrous web being maintained in a unified condition by means of tension in the second foraminous member sufficient to prevent lift-off of the composite structure at the nozzle.